The Truth About Planks - Good or Bad?

I’ve wanted to ask this question for a while now. It would be lovely if Kelli or Daniel could answer it but of course, everybody’s opinion is welcome.

I’ve seen a couple of videos on YouTube about the fact that doing planks is actually not good for you. The reasons (usually presented by very muscular guys with strong opinions) range from ’planks promote bad posture’, ’they aggravate back pain’ to ’they are just plain useless’. Many of the routines contain planks and I actually really like doing them. What’s the truth?